Over 100,000 persons per year in the U.S. are afflicted with cancer of the colon and rectum. When the number of colon/rectal cancers occurring each year is combined with the number of cancers occurring in other digestive organs, including the esophagus and stomach, such cancers of the digestive system account for more occurrences of cancer than any other single form of the disease. Contrary to many other forms of cancer, early diagnosis and treatment of digestive tract cancer does result in a cure rate of 80% to 90%. If, however, the disease is not detected until the later stages, the cure rate drops significantly. Thus, early detection of the disease is important to successful treatment of digestive tract cancer.
Most, but not all, cancers of the digestive tract bleed to a certain extent. This blood is deposited on and in fecal matter excreted from the digestive system. The presence of blood in fecal matter is not normally detected, however, until gross bleeding, that is, blood visible to the naked eye, occurs. Gross bleeding, however, is symptomatic of advanced cancers.
Digestive tract cancers in the early stages, including pre-cancerous polyps, also tend to bleed, giving rise to occult (hidden) blood in the fecal matter. Other pathological conditions, such as Crohn's disease and diverticulitis, can also give rise to the presence of occult blood in the fecal matter.
It is known that because of the relatively high fat content of fecal matter, blood, when present, is not distributed uniformly throughout it. For this reason, obtaining multiple samples from different areas of each bowel movement is desirable; but even a single positive test from any part of the feces should be considered a positive result.
Accordingly, test equipment and test procedures have been developed for use by physicians in testing for the presence of occult blood in fecal matter. One of the most successful tests is manufactured and sold by SmithKline Diagnostics of Sunnyvale, Calif. under the trademark HEMOCCULT and disclosed in Pagano U.S. Pat. No. 3,996,006, which is incorporated herein by reference in its entirety. In general, the Pagano test employs an absorbent paper impregnated with a guaiac reagent and encased in a special test slide having openable flaps on both sides of the test slide. To use the Pagano test slide, a sample of fecal matter is smeared onto the guaiac impregnated paper by opening the panel on one side of the test slide. Thereafter, the panel is closed. The panel on the opposite side of the test slide is then opened and a nonaqueous developing solution is applied to the guaiac impregnated paper. If occult blood is present in the fecal matter smeared on the opposite side of the paper, the guaiac reaction will dye the paper blue, providing a positive indication of the presence of blood in the fecal matter.
A drawback of this type of test is that a high percentage of false positives are obtained from patients who in fact do not have a cancer or other condition for which occult blood is symptomatic. For example, certain foods, such as rare red meat and peroxidase enzymes as present in certain foods, such as horseradish, broccoli and cantaloupe, can cause a false positive result.
To cut down on false positives, physicians place patients on specific diets designed to restrict the intake of animal proteins and other sources of false positives. Despite these efforts, large numbers of false positives still occur, as compliance with the restricted diet is unreliable. A false positive result in the test often results in expensive follow-up testing of patients who in fact have simply consumed a lot of meat or other undesirable foods just prior to the test.
A specific test for human hemoglobin has been devised. This test, offered by SmithKline Diagnostics under the tradename HEMESELECT, theoretically registers only human hemoglobin and not animal blood from meat or other agents, and therefore, theoretically does not require the patient to be on a special diet. While the hemoglobin test has the advantage over guaiac tests of registering only human hemoglobin, the hemoglobin test is expensive for a screening test and requires specially trained individuals to perform and read the test. Furthermore, hemoglobin tests are typically very sensitive, capable of detecting as little as 0.3 micrograms of blood, which is in excess of what a healthy normal person loses in fecal matter daily. Thus, because even healthy individuals lose a small amount of blood, which can be detected, a positive result may itself be a false positive leading to further costly, unnecessary test and procedures.
A need therefore exists for a relatively inexpensive test that has a minimal incidence of false positives and minimal manipulation of the specimen.